China’s newest stealth fighter prototype is made in the People’s Republic and could pose a challenge to U.S. air power. But it’s got an Achilles’ heel: Its engines are Russian imports.

Without reliable, homemade motors, China’s planned stealth armada will continue relying on Russian-made engines that aren’t always adequate — and in any event can be withheld by a wary Moscow.

“China’s inability to domestically mass-produce modern high-performance jet engines at a consistently high-quality standard is an enduring Achilles’ heel of the Chinese military aerospace sector,” wrote Andrew Erickson, a Naval War College analyst. Erickson chalked up the engine gap to a lack of standardization, cooperation and quality control in Chinese industry. …

China is reportedly spending $1.5 billion developing the homegrown WS-15 engine — a rough analogue to the F119 fitted to U.S. F-22 stealth fighters — to power future versions of the J-20, at least. China will probably take a similar approach with the J-21…. The new fighter could make do with inadequate Russian engines until a more powerful motor can be invented in China.